A service data transmission method and an apparatus are disclosed to reduce a data transmission latency. An example method includes: obtaining, by a first network device, first configuration information, where the first configuration information includes a first identifier and a first transmission mode corresponding to the first identifier, and the first transmission mode corresponding to the first identifier is a mode in which transmission is performed by using an access network; receiving, by the first network device, first service data and a second identifier that are sent by a terminal; determining, by the first network device based on the first identifier and the second identifier, that a transmission mode of the first service data is the first transmission mode; and transmitting, by the first network device, the first service data based on the first transmission mode.